This invention relates to a method for manufacturing dynamoelectric machines, and in particular relates to a method for manufacturing the magnetic frames for dynamoelectric machines.
More specifically, the present invention relates to a method for manufacturing the magnetic frames employed in dynamoelectic machines which are installed in electric vehicles of the low floor type, where the space available for installation is restricted, and so, to enable the required power output to be produced within that limited space, dynamoelectric machines of the type employing a tubular magnetic frame of polygonal cross-sectional configuration are generally used.
Typically dynamoelectric machines of the type employing a tubular magnetic frame of polygonal cross-sectional configuration, in their simplest form, have been constructed with a cross-sectionally polygonal tubular magnetic frame comprising a plurality of flat sides, to each of which is mounted a field device, such as a main pole field device or an interpole field device, each comprising a coil surrounding a magnetic core. Axially centrally of the magnetic frame is rotatably mounted an armature. In this simplest form dynamoelectric machine, the field devices are secured to smooth, regular, flat mounting surfaces machined on the respective sides of the polygonal magnetic frame, by mechanical means such as bolts which engage from outside the magnetic frame, through holes in the walls of the frame, with threaded holes formed in the respective field device magnetic cores, and which are tightened so as to hold the magnetic cores fast against the inner, mounting surfaces of the polygonal magnetic frame, for optimal magnetic contact between the magnetic cores and the magnetic frame.
To obtain the required degree of magnetic contact between the magnetic cores and the magnetic frame, and to ensure an accurate distance from the central axis of the dynamoelectric machine, it is the general practice to machine the inner field device mounting surfaces of the magnetic frame to provide substantially completely smooth, regular mounting surfaces at a precise distance from the central axis of the dynamoelectric machine. The field device magnetic cores themselves are generally made of stacked silicon steel plates, which plates are formed into the desired shape and size by stamping.
However, with the aforementioned simplest form dynamoelectric machine of the type with a polygonal tubular magnetic frame, the inner, mounting surfaces of the magnetic frame were flat, and the whole of the side had to be machined to provide the required smooth surface in the mounting area, thus requiring a considerable amount of time for the machining. Additionally, each side had to be machined individually, requiring time consuming repositioning and adjustment of the machining apparatus after the machining of each face. This added considerably to the overall time required for the machining operation, and also introduced the possibility of alignment errors during repositioning of the machining apparatus.
The prior art has, however, contemplated a reduction of the time required for machining the mounting surfaces by providing projections on the inner surfaces of the polygonal magnetic frame, which projections are smaller in area than the sides from which they project, and which form platforms or daises of suitable size for mounting the field device magnetic cores. With these projections, therefore, it became possible to reduce the time required for machining as only the mounting surfaces, the surfaces of the projections, needed to be machined.
These projections were, in the prior art, provided either by casting the polygonal magnetic frame as a unitary whole with integrally formed projections, or by manufacturing a polygonal tubular magnetic frame by welding together, at their respective ends, a number of flat sides, and then welding pieces to form projections to the respective sides.
The first mentioned of these methods of providing projections, however, had the considerable disadvantage that casting requires the use of a costly casting mold, thus adding substantially to the overall cost of the dynamoelectric machine. Additionally, disadvantages are to be found in that the casting process itself is a lengthy one.
And the second mentioned method of providing projections, although it eliminates the abovementioned disadvantages of costliness and time consumption of the first mentioned method using a casting mold, it introduces in their place the problem of structural distortions that develop as a result of the large number of welds that are necessary and the many places at which welding is carried out. Additionally, the number of welds involves the problem of time in the amount of time it takes to carry out a large number of welds.
Furthermore although the problem of machining time is reduced by means of providing projections, there still remains the difficulty of having to machine each individual surface separately, with a repositioning and realignment of the machining apparatus for each face, and the attendant possibility of alignment errors.